Sweet Fire by Jo Goodman

–1852,London; 1869, San Francisco, Samoa and Sydney, Australia–
Told all her life that she was plain, Lydia Chadwick knew no man would come courting. So it was with some suspicion that the shy, sweet, San Francisco heiress woke one morning with a tall, dark, dangerously handsome husband she couldn’t recall marrying. Lydia had lost her memory, and was desperate to discover if there was truly a love to remember. For as she looked at Nathan Hunter’s lean, muscular frame, she longed to abandon herself to the sensual stranger, and believe—if only for a little while—that the possessive passion in his smoky gray eyes was really for her.
Business and pleasure weren’t supposed to mix, but in this case Nathan Hunter was willing to make an exception. After all, it was in his best interests to keep his new bride’s mind off the secrets of her past and her hatred for him. Keeping focused on his goals proved difficult as Lydia’s sweet surrender wove a seductive spell around Nathan’s heart, arousing emotions he had thought forever buried.
But past transgressions have a way of catching up to the future. When Nathan’s former friend and rival, Brigham More, seemingly returns from the dead, he stands to ruin Lydia and Nathan by unleashing an unspeakable secret.